More fool him: I scraped a decent grade and have now (decades later) done math[s] modules at degree level.

Unless, that was his plan all along, to try and shame me into putting some effort in?

But, again, not the point of Freya's original point, nor of my posting of it.

But the program does not terminate.

So the program cannot answer *either*, so it's not "just a for loop"

The point is that there is a translation from the notation to a computer language format that allows a person not versed in maths to understand the underlying concept of the math notation in an intuitive way, as a starting point. If you can't understand what sigma does at its most basic, you cannot understand its actual math purpose as a whole.

Now if you had left the starting index out of the notation, that would have been a stumper

I ended up in computers instead which totally has no maths whatsoever!

(in hindsight, not the best maths teacher)

But in general, the sigma is the abstract definition, the for-loop is a possible concrete implementation of that definition, in a language that the target of this PSA (non mathy programmers) can understand and go "oooh ok I get it now". It would have saved me like half a semester if someone had shown me this up front, no other words needed.

Borring from the field of computer science to remove all the greek characters that often have multiple uses [1] and rename operators with descriptors could make it way more accessible.

[1] Okay this is mainly astrophysics's fault that one equation used sigma in both cases for three different things.

OOOOOOOOOOOH! I've *always* wondered!!

As an analogy to convey some information is fine, I'm just reminding that it ain't the same thing.

This is life-changing for me.